The present invention relates to plug valves and, more particularly, to tapered plug valves.
Experimentation has been directed to reducing and/or eliminating the lockup phenomenon as applied to said tapered plug valves. The basic thrust of this experimentation is directed to the elimination of the interference lockup or pinching believed to be critical when a tapered plug valve is in the open or partially open position. It has been found and is generally believed that a pressure pulse in the line in which the valve is connected and/or the weight of the plug when unfavorably orientated will first cause sticking; then if the line pressure is reduced, an interface pressure is created which will give rise to a high frictional resistance between the casing and the plug thus rendering the valve extremely difficult to close. The need has become apparent therefore for a tapered plug valve in which hydraulic and/or gravitational forces exerted on the plug with a finite component toward the cone or taper apex are eliminated.